The present invention concerns a method and apparatus for physically separating gaseous mixtures of matter, particularly isotopes, wherein at least one beam of a polarized electromagnetic wave is directed through such a mixture and the frequency or wave length, of the electromagnetic wave is adjusted so that the dipole behavior of the individual components of the mixture, is selectively and differently influenced and the isotopes are segregated by the electric and/or magnetic field of the beam. As it does also in other separating methods, the problem arises here to increase the separating performance or the throughput and to optimize them with respect to the power to be supplied, a laser normally being used to provide the wave or beam.